A motor is a machine that obtains a rotational force from electric energy and includes a stator and a rotor. The rotor is arranged inside or outside the stator and is configured to electromagnetically interact with the stator. The rotor is rotated by a force acting between a magnetic field and a current flowing through a coil.
Permanent magnet motors using a permanent magnet to generate a magnetic field may be classified into a surface-mounted permanent magnet motor, an interior type permanent magnet motor and a spoke type permanent magnet motor. Among them, the spoke type permanent magnet motor structurally has a high magnetic flux concentration degree. Therefore, the spoke type permanent magnet motor is capable of generating a high torque and a high output and can be reduced in size for the same output. Therefore, the spoke type permanent magnet motor may be usefully applied to a driving motor for a washing machine, a driving motor for an electric vehicle, a driving motor for a small-sized generator, and the like, which require high torque and high output characteristics.
Such a spoke type permanent magnet motor generally includes permanent magnets arranged radially around a shaft of the motor and a rotor core provided so as to support the permanent magnets and form a passage of the magnetic flux. The rotor core supports the permanent magnets by means of rotor poles protruding from the periphery of the shaft. However, when the connection portions between the rotor poles and the periphery of the shaft are formed thick, the magnetic flux is leaked through the connection portions, whereby the efficiency of the motor may be reduced. Therefore, in order to enhance the efficiency of the motor, it is important to form the connection portions thin.
However, in the case of thinly forming the connection portions, the structural strength of the rotor core is reduced. This may pose a problem that the rotor core is deformed or damaged during the process of high speed rotation of the rotor. In addition, the rotor poles may be loosened and may be unable to strongly support the permanent magnets. Thus, the permanent magnets may be separated from the rotor core by the centrifugal force generated by rotation.